When diving in cold water, a diver can stay down for only a short period unless some type of heating is provided. One very successful type of heated suit is disclosed in U.S. Pat. No. 3,449,761, entitled "Heated Underwater Diving Suit". The associated hot water supply for the suit is described in U.S. Pat. No. 3,762,392, entitled "Hot Water Heater System for Divers". The suit is provided with valves for controlling heat and its distribution and the added comfort enables a diver to operate in cold water for a considerable length of time. However, the breathing gas, supplied from the surface along with the hot water, passes through a considerable length of hose exposed to the cold water. Insulation of the entire hose is impractical, but breathing the cold gas can be uncomfortable for the diver. Some form of heating the breathing gas, preferably without an additional power source, would be a great advantage in prolonging operating time of a diver.